This invention relates generally to an ignition spark timing control system, and more particularly to a system having magnetic sensing capabilities for timing the ignition to the engine shaft position.
Virtually all internal combustion engines manufactured today include an electronic control unit which monitors and controls ignition timing. Functions which were once controlled through various mechanical linkages are increasingly controlled in the electronic control unit. With this control arrangement, timing of engine spark and fuel injection functions with the valve of each cylinder can be precisely controlled. This precision provides greater efficiency and responsiveness of the engine to varying conditions of operation.
Distributor sensors used today typically produce one pulse, or one rising edge, for each spark plug to be fired.
Many currently used distributors do not provide information required to control the fuel injection system. Further, such systems do not provide information to the electronic control unit to indicate which spark plug is being fired. In such systems, the electronic control unit controls spark advance with respect to valve and fuel injector timing by estimating engine speed between sensor signals and delaying the spark for a calculated time after a sensor signal has been received.
Okada et al, in U.S. Pat. No. 4,742,811, disclosed an ignition timing control system using three axially adjacent columns of magnets attached to a shaft. Each magnet column rotates in relation to a Hall-sensor which generates a signal at various degrees of shaft rotation. The first row of magnets is symmetrically spaced about the column. The second row is asymetrically spaced; while the third row is symmetrically spaced, but has one pulse which is differentiated from the others by very small pole reversals at the end of the pulse. Processing of these three signals through the electronic control unit provides the discrimination capability necessary to proper functioning of the system.
The disposition of the magnetic columns one above the other in the Okada patent requires a substantial minimum height for the assembly described. Moreover, the twenty-four symmetrical poles in the first column indicates that each pole is subtending an angle of fifteen degrees on the circumference of the column. This rather large pulse to angle equivalence acts to limit the precision of the device function. The imprecision is overcome by the use of three magnetized columns rather than the lesser number.
U.S. Pat. No. 3,373,729, to Lemen, discloses an electronic ignition system for internal combustion engines which uses a disk having a plurality of equally spaced magnets about its periphery. The disk is sawed perpendicular to its axis to form a slot having axially opposed magnets in the disk periphery on both sides of the slot. A Hall-sensor placed within the slot generates triggering signals according to the fluctuating magnetic field experienced as the disk rotates. This device, in essence, serves to replace the breaker points found in the distributor of a standard mechanically timed ignition system. Thus, this invention eliminates the mechanical contact points together with their shortcomings, but it does not improve the accuracy of the ignition and fuel injection timing.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.